A combined biochemical and anatomical study is underway to identify chemical neurotransmitters in retinal neurons and in neurons of the visual pathway, to examine the development of neurotransmitter systems in retina, and to determine the role of chemical neurotransmitters in the processing of visual information. Two systems are being investigated: (1) the relatively simple visual system of Limulus polyphemus and (2) developing mammalian retinal neurons in intact retinas and in monolayer cell culture. Work with the simple visual system has led to the identification of the biogenic amine octopamine as a neurotransmitter released from retinal efferent fibers; i.e. fibers which originate from cells in the brain and innervate the retina. Our studies suggest that this amine may alter visual sensitivity and may be important in maintaining normal photoreceptor cell function. Studies of the intact developing retina have shown that at least two neurotransmitters, GABA and acetylcholine appear very early in normal retinal development. The regulation of development of these two neurotransmitter systems is being investigated using monolayer cell cultures.